1. Field of the Disclosure
Embodiments disclosed herein relate generally to wedge thread connections. More particularly, embodiments disclosed herein relate to wedge threads having a solid lubricant coating permanently bonded thereon and related methods of permanently bonding the solid lubricant coating on the wedge threads.
2. Background Art
One type of threaded connection commonly used in oil country tubular goods is known as a wedge thread. Referring initially to FIGS. 1A and 1B, a prior art tubular connection 100 having a wedge thread is shown. As used herein, “wedge threads” are threads, regardless of a particular thread form, that increase in width (i.e., axial distance between load flanks 225 and 226 and stab flanks 232 and 231) in opposite directions on a pin member 101 and a box member 102. The rate at which the threads change in width along the connection is defined by a variable known as the “wedge ratio.” As used herein, “wedge ratio,” although technically not a ratio, refers to the difference between the stab flank lead and the load flank lead, which causes the width of the threads to vary along the connection. Furthermore, as used herein, a thread “lead” refers to the differential distance between components of a thread on consecutive threads. As such, the “stab lead” is the distance between stab flanks of consecutive thread pitches along the axial length of the connection.
A detailed discussion of wedge ratios is provided in U.S. Pat. No. 6,206,436, issued to Mallis, assigned to the assignee of the present disclosure, and incorporated by reference in its entirety herein. Furthermore, wedge threads are extensively disclosed in U.S. Pat. No. RE 30,647 issued to Blose, U.S. Pat. No. RE 34,467 issued to Reeves, U.S. Pat. No. 4,703,954 issued to Ortloff, and U.S. Pat. No. 5,454,605 issued to Mott, all assigned to the assignee of the present disclosure and incorporated herein by reference in their entirety.
Referring still to FIGS. 1A and 1B, in wedge threads, a thread seal may be accomplished through contact pressure caused by interference that occurs at make-up over at least a portion of connection 100 between pin load flank 226 and box load flank 225 and between pin stab flank 232 and box stab flank 231. Close proximity or interference between roots 292 and 221 and crests 222 and 291 complete the thread seal when occurring proximate to such flank interference. Generally, higher pressures may be contained either by increasing interference between the roots and crests (“root/crest interference”) on pin member 101 and box member 102 or by increasing the aforementioned flank interference.
Prior to make-up, a flowing joint compound commonly referred to as “pipe dope” is typically applied to surfaces of a threaded connection to improve the thread seals and provide lubrication during make-up of the connection. For example, the pipe dope may assist a wedge-threaded connection in achieving a thread seal between load and stab flanks thereof, e.g., as disclosed in U.S. Pat. No. RE 34,467 issued to Reeves. Further, pipe dope may protect the threads of the pin and box members from friction galling during make-up and break-out.
A flowing joint compound such as pipe dope may be used in wedge thread connections because of the close-fitting manner in which wedge threads make-up. As previously mentioned, wedge threads rely on a full surface contact theory, which means that each contact surface, i.e., corresponding roots/crests and stab and load flank surfaces are either in close proximity or full interference. Thus, due to the tight-fitting characteristics of wedge threads from multiple thread surface interferences, a pipe dope is used so that as the connection is made up and corresponding thread surfaces come together, the pipe dope may be squeezed out so as not to impede the proper engagement of the thread surfaces.
The use of pipe dope in wedge thread connections is not without certain deficiencies. When a wedge thread connection is made-up, excess pipe dope may become trapped (rather than being squeezed out) between the pin threads and the box threads, which may either cause false elevated torque readings (leading to insufficient make-up or “stand-off”) or, in certain circumstances, damage the connection. Attempts to mitigate pipe stand-off have come in the form of providing features in the thread form to reduce a build-up in pressure of pipe dope used in the make-up of the threaded connections, e.g., U.S. Publication No. 2008/0054633, assigned to the assignee of the present application and incorporated herein by reference in its entirety. In addition, problems associated with excess pipe dope on wedge-threaded connections may be avoided by restricting the amount of pipe dope applied and by controlling the speed at which the wedge-threaded connection is made-up. Limiting the make-up speed of a wedge-threaded connection allows the pipe dope to travel and squeeze out before it becomes trapped within the connection at high pressures. However, limiting the make-up speed of the connection slows down the overall process of assembling the drillstring.
Pipe stand-off due to inadequate evacuation of pipe dope is detrimental to the structural integrity of wedge thread connections. As the pressure build-up may bleed off during use, the connection is at risk of accidentally backing-off during use. Therefore, stand-off in wedge thread connections is of particular concern as it may lead to loss of seal integrity or even mechanical separation of two connected members. Furthermore, pipe stand-off may be particularly problematic in strings used at elevated downhole service temperatures (i.e., the temperature a tubular would be expected to experience in service). Particularly, in high temperature service (e.g., temperatures greater than 250° F., a steam-flood string, or a geothermal string), even a small amount of stand-off may be deleterious. For example, if a made up wedge thread connection having even an infinitesimal amount of stand-off is deployed to a high temperature well, the pipe dope may flow out of the wedge thread connection, thus reducing the integrity of the thread seal. Further, use of a flowing pipe dope in wedge threads may lead to thread seal leaks, particularly at elevated pressures, as the viscosity of the pipe dope increases.
Larger OD wedge threads, which utilize pipe dope, may typically require a second application of torque to insure a complete make-up of the threaded connection. Because of the length and configuration of the wedge thread, the larger diameter connections may be susceptible to hydraulic lock and require extra torque to push the thread dope (i.e., force the thread dope to flow) along the length of the connection. Such a procedure is commonly known as “double bumping” a connection because torque is applied a number of times to “squeeze” the pipe dope along the threads. Notably, double bumping increases connection make-up time.
Accordingly, there exists a need for a thread lubricant capable of being used in tight-fitting wedge thread connections that substantially reduces pipe stand-off concerns and is effective at elevated downhole temperatures.